(1) Field of the Invention
This invention concerns Cu-Al-Ni shape memory alloys and, more specifioally, it relates to the improvement in the workability of the shape memory alloys of the above-mentioned type by the modification to the alloy composition.
(2) Description of the Prior Art
In the field of the shape memory alloys, there exist problems for the development of novel alloys and for finding new application uses thereof, which stimulate to each other such that possible application uses are sought for newly developed alloy and, vice versa, new alloys are demanded for expected uses. Among the shape memory alloys having thus been developed, AuCd, Cu-Zn-Al, Cu-Al-Ni and the like have been noted as being comparable with the Ti-Ni type alloys. Particularly, the latter two Cu type alloys are generally considered prominent in view of their low cost. When comparing the two Cu type alloys with each other, Cu-Al-Ni alloy is superior both in the shape memory performance and heat stability (heat resistivity) and attracts general attention. However, the defect in the Cu-Al-Ni alloy of low cold workability somewhat hinders the trend for the exploitation of its application uses. The present inventors, considering such a situation, have already found that the workability of the Cu-Al-Ni alloy can be improved by blending Ti therewith to render the crystal grain finder and disclosed such a finding in Japanese Patent Laid-Open No. 167737/1983.
While the effect of improving the workability disclosed in our invention is due to the refinement of the grain by the blend of Ti and provides a usefulness in the practical point of view, a considerable room seems to be left for the improvement in view of the metal structure. That is, aside from the property of the .beta. phase itself in the Cu-Al type alloy, the difficulty upon fabrication of the Cu type alloy is attributable, to the fact that the intermetallic compound .gamma.2 phase tends to be deposited as the secondary phase because the Al content lies on the side of the hyper-eutectoid alloy region in the Cu-Al-Ni alloy.
Based on the above-mentioned considerations, we have reached an idea that it is important, for the improvement in the workability of the Cu-Al-Ni alloy, to restrict the hardness by suppressing the deposition of the intermetallic compound 2 phase as low as possible and rendering the grain size as fine as possible. This invention has been accomplished on the basis of such concept, and by realizing the concept along with the modification in the alloy composition.